Many types of natural and synthetic roofing materials are available in the market. Some of the more popular natural types include natural slate, shakes and shingles. Natural slate has long been a popular roofing material due to its attractive appearance and durability and also because it possesses other highly desirable properties such as being fireproof and waterproof. It is, however, very expensive and as a result is normally used for roofing in only the most expensive houses and in other structures where the increased cost can be justified. Slate is a brittle material and can be cracked or broken rather easily. Natural slate tiles are quite durable; however they require a substantial amount of labor in their installation and can break on impact. They are inherently fragile and suffer much breakage during shipping and installation. They are fragile even after installation on the roof and can be damaged by foot traffic on the roof. Slate tiles tend to be excessively heavy and dangerous in earthquakes and high winds, and will fall through the roof in the event of a fire. Since the tiles are so heavy, they are also expensive to ship. Also, due to the weight of natural slate, extra structural support is required for slate roofs compared to cedar shake or shingle roofs or asphalt roofs.
Wood shakes and shingles are subject to breakage, rot and loss of coloration. Their cost is relatively high and they are labor-intensive to install. Furthermore, wood shakes and shingles can be relatively heavy and are flammable, porous and cannot withstand relatively high wind velocity. A disadvantage of wooden shakes and shingles is that they absorb moisture and swell. Therefore, they must be applied in a spaced-apart arrangement to allow room for moisture expansion. Because of the propensity of wooden shakes and shingles to absorb water, with time they tend to curl and not remain flat on the roof.
Synthetic roofing materials provide some advantages over these natural materials. They are moldable and light in weight. However, they have not, in general, been fully acceptable in terms of performance because they often do not meet all the requirements desired for roofing applications. As an example, synthetic roofing materials typically have high concentrations of plastic or rubber content in the formulation that directly effects the fire resistance of the products because plastic and rubber materials lack fire resistant properties. In some case, fire resistance of the product has been enhanced by adding a high concentration of flame retardant, which in turn, makes the product much more expensive. Products with recycled rubber may also have a strong odor on warm days due to the gassing off of volatile components.
One desirable property of any synthetic roofing material is to be able to resist fires. This is particularly true in regions having a hot and dry climate, although fire resistance is desirable everywhere. A particularly important aspect of fire resistance is the ability of the roofing material to prevent the spread of fire from a source of heat, such as a burning ember, from burning through the roof to thereby expose the roof deck or interior of the building to a fire.
Another desirable property of any roofing material is that it has long-term ductility, enabling installers and owners to walk on the roof at any time during the roofing product's lifespan, without causing damage. Ductility in roofing materials also allows repairs to be more easily undertaken in the event of damage, such as that incurred from falling tree limbs.
Additionally, with public awareness increasing about the importance of recycling to consume fewer materials, it is desirable that recycled materials be used as a portion of any synthetic roofing materials. This provides a market for recycled materials, and recycling practices are encouraged if there is a known commercial application for these materials.
There have been various attempts to meet the requirements of synthetic building materials by means of molded products made from plastic resins and inorganic fillers. The following patent documents are examples.
U.S. Pat. No. 5,571,868 (Datta et al.) discloses elastomeric polymer compositions used in sheet materials for roofing. The materials can comprise elastomeric polymers and inorganic fillers, and can be made by heating, roll milling and calendering the mixture.
U.S. Pat. No. 3,070,577 (Gessler et al.) discloses polymeric composites containing inorganic fillers. The mixture may be formed into thin sheets, useful for roofing, by heating it and passing it through rollers.
U.S. Pat. No. 4,263,186 (Bluemel) discloses a thermoplastic composite made by mixing polyethylene and calcium carbonate. It may be formed into a sheet on a rolling mill and the resulting material used in building construction.
US 2005/0140041 A1 (Seth) discloses a synthetic building material made by extruding a mixture of plastic resin, which may be recycled polyethylene, and a filler, which may be limestone.
U.S. Pat. No. 3,976,612 (Kaji et al.) discloses a method of making a composite sheet by mixing an inorganic calcium compound with polyethyelene, kneading and heating the mixture into a paste and calendering it into a film.
GB 1 534 128, published Nov. 29, 1978, discloses a method of making a composite sheet comprising polymer resins and calcium carbonate by heating the composition, rolling it into a rough film at a temperature of 160 to 180 degrees C. through a roller nip of 2-5 mm and rolling the rough film into a smooth film at a temperature of 160 to 180 degrees C. through a roller nip of 0.1 to 1 mm.
However, there remains a need in the building industry for a synthetic sheet material which has the characteristics that are important for use in roofing and siding applications. It would be desirable to have a synthetic material that could overcome the disadvantages of the previous attempts to produce such materials. There is a need for a synthetic sheet material that is durable, moderate in weight, inexpensive, fire resistant, tough and ductile, that can be made in part by using recycled materials, and that can be produced using relatively inexpensive production equipment.